Throughout her presidential campaign, Democratic candidate Hillary Clinton has had to deal with controversy and scandal.

With the opening of the Democratic National Convention in Philadelphia on Monday, she found herself facing questions about certain payment sources for her husband’s speaking fees.

In 2009, former President Bill Clinton spoke at an event held by the Lady Taverners in London. His speech helped to raise a substantial amount for a charity the group supports.

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According to The Washington Free Beacon, Hillary Clinton, then secretary of state, reported in federal financial filings that her husband’s $290,000 speaker’s fee had been paid by “World Management Limited.”

In actuality, it had been financed by Robert Whitten, a wealthy British businessman.

Whitten was facing obstacles with the United Nations Educational, Scientific and Cultural Organization’s World Heritage Committee concerning a project to build a development in St. Lucia on land that is protected.

The State Department is responsible for overseeing U.S. policy with UNESCO, and the United States provides 25 percent of the organization’s funding.

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The Free Beacon investigated Bill Clinton’s speaking fee payments and found that although records from Hillary Clinton name small foreign firms as the origin of his fees, the actual payments were made by anonymous third parties.

Watchdog groups call the Clintons’ handling of this information “troubling,” adding it hides the source of the payments.

Ken Boehm, chairman of the National Legal and Policy Center, said the Clintons’ practices “suggest secrecy and non-transparency.”

“The tens of millions in speaking fees going directly to the Clintons should be completely transparent,” he said. “Anything less suggests unethical conduct.”

The Senate agrees with Boehm’s assertion.

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In an advisory on federal disclosure filings, the Senate stated, “For payments which are received by an individual through a speaker’s bureau, list the actual payer as the source.”

There have been other instances where the origin of speaking fees have been questioned.

Fox News reported in July 2015 that a “mystery donor” paid Bill Clinton’s $150,000 fee for speaking to the Radiological Society of North America.

Some of Hillary Clinton’s speaking fees have also been questioned.

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A report by The Huffington Post in May revealed that a speech she gave in Canada was predominately bankrolled by two banks that promoted the Keystone XL pipeline, while records show the funds coming from a promotional company called tinePUblic Inc.